replace reusePort by failOnExistingPort, simpler state (single bool), no TOCTOU for numThreads=1

httpbeast.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "0.4.0"
+version       = "0.5.0"
 author        = "Dominik Picheta"
 description   = "A super-fast epoll-backed and parallel HTTP server."
 license       = "MIT"

src/httpbeast.nim

@@ -54,9 +54,10 @@ type
     domain*: Domain
     numThreads: int
     loggers: seq[Logger]
-    reusePort: bool
-      ## controls whether to fail with "Address already in use".
-      ## Setting this to false will raise when `threads` are on.
+    failOnExistingPort: bool
+      ## Fail with "Address already in use" if port is in use, by attempting
+      ## to bind to a temporary socket to fail early if `numThreads>1`, or
+      ## not setting `OptReusePort` if `numThreads==1`.
 
   HttpBeastDefect* = ref object of Defect
 
@@ -67,14 +68,14 @@ proc initSettings*(port: Port = Port(8080),
                    bindAddr: string = "",
                    numThreads: int = 0,
                    domain = Domain.AF_INET,
-                   reusePort = true): Settings =
+                   failOnExistingPort = true): Settings =
   Settings(
     port: port,
     bindAddr: bindAddr,
     domain: domain,
     numThreads: numThreads,
     loggers: getHandlers(),
-    reusePort: reusePort,
+    failOnExistingPort: failOnExistingPort,
   )
 
 proc initData(fdKind: FdKind, ip = ""): Data =
@@ -311,6 +312,12 @@ proc updateDate(fd: AsyncFD): bool =
   result = false # Returning true signifies we want timer to stop.
   serverDate = now().utc().format("ddd, dd MMM yyyy HH:mm:ss 'GMT'")
 
+proc newSocketAux(settings: Settings): owned(Socket) =
+  result = newSocket(settings.domain)
+  result.setSockOpt(OptReuseAddr, true)
+  result.setSockOpt(OptReusePort, not settings.failOnExistingPort)
+  result.bindAddr(settings.port, settings.bindAddr)
+
 proc eventLoop(params: (OnRequest, Settings)) =
   let (onRequest, settings) = params
 
@@ -319,12 +326,7 @@ proc eventLoop(params: (OnRequest, Settings)) =
 
   let selector = newSelector[Data]()
 
-  let server = newSocket(settings.domain)
-  server.setSockOpt(OptReuseAddr, true)
-  if compileOption("threads") and not settings.reusePort:
-    raise HttpBeastDefect(msg: "--threads:on requires reusePort to be enabled in settings")
-  server.setSockOpt(OptReusePort, settings.reusePort)
-  server.bindAddr(settings.port, settings.bindAddr)
+  let server = newSocketAux(settings)
   server.listen()
   server.getFd().setBlocking(false)
   selector.registerHandle(server.getFd(), {Event.Read}, initData(Server))
@@ -476,6 +478,10 @@ proc run*(onRequest: OnRequest, settings: Settings) =
 
   echo("Starting ", numThreads, " threads")
   if numThreads > 1:
+    if settings.failOnExistingPort:
+      close(newSocketAux(settings)) # attempt to bind to a temporary socket
+    var settings = settings
+    settings.failOnExistingPort = false
     when compileOption("threads"):
       var threads = newSeq[Thread[(OnRequest, Settings)]](numThreads)
       for i in 0 ..< numThreads: